Aging has an enormous negative impact on the cerebral circulation. One of the primary mechanisms thought to underlie many of the major changes that occur with aging involves oxidative stress. The overall goal of this project is to define molecular mechanisms which protect the cerebral vasculature from oxidative stress and dysfunction during aging. Although cerebral vascular disease, stroke, and vascular dementia all increase markedly with age, almost nothing is known regarding the importance of oxidative stress in the cerebral circulation with aging. In preliminary data, we observed superoxide-mediated vascular dysfunction during aging that was of greater magnitude and occurred earlier in cerebral arteries than in the carotid artery or aorta. Our first Aim is to test the hypothesis that oxidative stress plays a major role in mediating this dysfunction. Peroxisome proliferator activated receptors (PPARs) are transcription factors that may produce antioxidant effects. The role of PPARy in the cerebral circulation is not known. Our second Aim is to examine the hypothesis that PPARy protects the cerebral vasculature under normal conditions and during aging. Using a mouse expressing a human dominant negative mutation in PPARy, a 'humanized'mouse, we have obtained preliminary evidence that PPARy exerts major protective effects in cerebral blood vessels. We will determine if oxidative stress contributes to impairment of vascular function in adult mice expressing this dominant negative form of PPARy. We will also determine if a synthetic activator of PPARy or genetic overexpression of wild-type PPARy in endothelium decreases oxidative stress and improves vascular function in aging. One mechanism by which oxidative stress may produce vascular dysfunction involves asymmetric dimethylarginine (ADMA), an endogenous inhibitor of endothelial NO synthase. In Aim 3, we will use mice overexpressing the ADMA hydrolyzing enzyme, dimethylarginine dimethylaminohydrolase, to test the hypothesis that aging produces adverse vascular effects through an ADMA-dependent mechanism. Our preliminary data support these hypotheses. Because synthetic activators of PPARy are already approved for clinical use, this area of basic research has implications for translational medicine. Our focus on mechanisms of oxidative stress and endothelial dysfunction seems appropriate since endothelial dysfunction has a major impact on the vessel wall and has emerged as an independent predictor of clinical events. These studies should provide new insight into mechanisms of vascular protection during aging and fit well within several major themes of this program - cardiovascular risk factors, oxidative stress, and mechanisms of vascular protection.